Question

I have a page where you basically select a set of options (configuration), and then you go to a next page, where you do some stuff
Using the MVVM Light toolkit, I have a viewmodel that binds to the view of the first page. when the user hits a button, it redirects to another view, which would be the 2nd page
i.e.:

Page2Command = new DelegateCommand((obj) => 
    Messenger.Default.Send<Uri>(new Uri("/DoStuffView.xaml", UriKind.Relative), 
                                Common.CommonResources.GoToDoStuffRequest)) });

The problem is, the viewmodel for the 2nd view (the way that I see it) has a couple of parameters in the constructor, which are basically the dependencies on the configuration that was set on the first page.

i.e. :

public DoStuffViewModel(ICollection<Note> availableNotes, SoundMappers soundType)
{
}

The problem lies here.. How can I instantiate the viewmodel with this data that was dynamically selected by the user on the 1st page?.
I can’t use the ViewModelLocator pattern that MVVM light provides, since those viewmodels don’t have any dependencies, they are just by themselves (or they can retrieve data from a db, file or whatever, but they don’t have any dynamic input data). I could do it through the view’s constructor, instantiate there the viewmodel, and assign to the view’s DataSource the newly created viewmodel, but I think that’s not very nice to do.
suggestions?

Answer 1

As I see you send messsage using Messenger class so you are familiar with messaging in MVVM light. You have to define your own message type that should accept your parameters from page 1:

    public class Page2ViewModelCreateMessage : MessageBase
{
    public ICollection<Note> AvailableNotes{get;set;}
    public SoundMappers SoundType{get;set;}

    public Page2ViewModelCreateMessage ()
    {

    }

    public Page2ViewModelCreateMessage(ICollection<Note> availableNotes, SoundMappers soundType)
    {
        this.AvailableNotes = availableNotes;
        this.SoundType = soundType;
    }
}

You have to send an Page2ViewModelCreateMessage instance with you parameters and send it on navigating:

var message = new Page2ViewModelCreateMessage(myAvailableNotes, mySoundType)
Messenger.Default.Send(message);

On Page2 you have to register for recieving message of type Page2ViewModelCreateMessage:

        Messenger.Default.Register<Page2ViewModelCreateMessage>(this, OnPage2ViewModelCreateMessage);
    ..
    public void OnPage2ViewModelCreateMessage(Page2ViewModelCreateMessage message)
    {
        var page2ViewModel = new Page2ViewModel(messsage.AvailableNotes, message.SoundType);
    }   

As you can see I have replace your DoStuffViewModel with Page2ViewModel to be more clear.

I hope this will help you.

NOTE:I dont guarantee that code will work as its written in notepad.